(1) Field of the Invention
The invention relates to the general area of integrated circuits, more particularly to fuses for use in those technologies.
(2) Description of the Prior Art
Fuses are used in integrated circuits as a means for breaking connections under controlled conditions. A convenient way to activate a fuse (change its resistance from short to open circuit) is to briefly irradiate it with a laser pulse. This causes the fuse element to heat up to an extent sufficient to disintegrate it but not enough to affect neighbouring parts of the integrated circuit.
Typically, the fuse will consist of a short length of a conductive layer, most commonly heavily doped silicon. Until the fuse is activated (which may be never) it needs to be protected from the environment along with all the other parts of the circuit. To this end it is covered by a fuse window--a layer of passivating material that is transparent to the activating laser radiation.
It is important that the fuse window be clear, be accurately aligned with the fuse element, and allow radiation to reach as large a portion of the fuse as possible.